Influence of the intermediate oxidation layer on the characteristics of lead zirconate titanate thin films with aluminium substrate

This paper presents a flexible piezoelectric device that has been realized by depositing lead zirconate titanate (PZT) thin films by chemical solution deposition (CSD) on a commercial aluminum foil as a substrate. The thermal treatment required for the crystallization of the PZT thin films leads to the oxidation of the substrate and a parasitic intermediate layer of alumina (Al2O3) is formed between the substrate and the first PZT layer. The comparison with and without the use of a conductive ruthenium dioxide (RuO2) interlayer, which can shunt the insulating alumina layer, showed the influence of the latter on the different characteristics of the material. The thickness of the alumina layer on the surface of the aluminum substrate after deposition of the PZT film (approximate to 39 nm) was determined by calculation and confirmed by transmission electron microscopy (TEM). Dielectric characterization of the sample without considering this layer gives the permittivity of the Al2O3/PZT bilayer and not the active material alone (PZT). A relative permittivity value of 313 is measured against 558 for the single PZT layer if the alumina layer is taken into account, which means a decrease of 44%. The piezoelectric characterization is also influenced by the alumina layer, the piezoelectric coefficient is 14 pC/N while it is 26 pC/N when this layer is taken into account. This study evidences and quantitatively evaluates the influence of the oxidation layer (Al2O3) on the dielectric and piezoelectric characteristics and mechanical energy harvesting performances.